PSU > How Much Power!?i

thegoonden said:
That's one scary cooker!


We used to run out stage rig, some 30+ devices, from a single plug, and no problems at all, as total consumption was less that 1000W.
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You've confused me now :) I thought, based on the posts above. You could go upto 3000w based on a 13amp fuse?
 
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james.miller said:
fuses limit the current a device can pull. they are there to limit the device in such a situation that there is a problem and the device pulls too much current which could damage it and/or other things plugged in. the fuse is there to stop that from happening.
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This is incorrect, the fuse is simply there to protect the cable.
 
Super_Sonic said:
This is incorrect, the fuse is simply there to protect the cable.
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not exactly. an appliance could well destroy itself and combust pulling only 4 or 5 amps when the cable itself would have handled twice that. assume the worst case scenario, appliance combusts, fire spreads up the mains lead....the fuse isnt going to stop anything now, but had it been fused for the appliance in question, it might well have stopped the accident in the first place.
 
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No offence mate but I'm a qualified electrician and I'm telling you now that the fuse's in plugs were designed to protect the cable and nothing else!
A BS 1362 fuse (plug fuse) is not quick enough to protect a device in the vast majority of case’s you describe, this is why most electronic/electrical devices contain quick blow fuse's as they stand a far greater chance of protecting the device for permanent damage.

The BS 1362 fuse is simply there to so that when the cable is overloaded it blows and does not allow the cable to get hot and burn your house down!

Also the reason you cannot draw as much current from a extension lead that’s not fully unwound is because of magnetic induction generated by the coils of cable that have current flowing through them, this is how transformers work.
 
Super_Sonic said:
No offence mate but I'm a qualified electrician and I'm telling you now that the fuse's in plugs were designed to protect the cable and nothing else!
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good for you lol:p i wasnt originally talking about BS1362's in a 3 pin plug but lets clear this up now then. a good question - why use different fuses at all (other than 13amp) if you are only fusing for the mains lead. as a qualified electrician, could you tell us?

i already know it has something to do with flex. but a further question, why then would you find say.....a kettle lead, with a 3 or 5amp fuse? they arent traditionally flexible cables anyway and arent thin either, not like somethign on a high current device like an electric blanket or somethign similar. for example, i believe my ps3 comes with a 3amp kettle lead - is that 3amp fuse needed to protect the lead over a 13a fuse?
 
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james.miller said:
good for you lol:p i wasnt originally talking about BS1362's in a 3 pin plug but lets clear this up now then. a good question - why use different fuses at all (other than 13amp) if you are only fusing for the mains lead. as a qualified electrician, could you tell us?
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:confused:
Because not all power leads are capable of supplying 13A of current!
Look at a european power lead and you will see that many are 0.75mm2 which is not a safe CSA for supplying that amount of current for any length of time.

Some accessories require protection at a lower current than that provided by the ring final protection device. The protection device used in such accessories is a 25 mm ceramic cartridge fuse, rated at 3 A, 5 A, or 13 A.

In the case of permanently connected equipment the fuse is contained in a holder mounted in an accessory known as a fused spur box, which usually includes an isolator switch and often a neon bulb to indicate if the equipment is powered. In this case the fuse protects the spur (equipment supply) cable and any switch contacts.

In the case of non-permanently connected domestic equipment, a socket rated at 13 A is attached to the ring final, into which a fused plug may be inserted. The fuse protects the contacts (including any switch contacts) and the equipment flex. There are two benefits to this arrangement. Firstly with low power equipment a flex with a low current rating (and therefore minimal diameter) can be used. Secondly, if the equipment is moved to a different socket, it will remain protected by the same (hopefully correct) fuse. The disadvantage is that despite warnings to the contrary people often use a fuse rated at too high a current, or even wrap a blown fuse in aluminium foil, meaning that under fault conditions the contacts and flex will be subjected to anything up to the maximum ring main current. This is likely to cause a fire.

Note that the equipment itself should have its own protection measures, such as another fuse, unless the plug or accessory fuse affords all required protection (as is the case with most table lamps, for example). It is also important to be aware that when a double socket is rated at 13A this applies to the total rating of the two sockets together, and in this case the use of a 13 A-rated double socket (e.g. a "free double socket" on an extension lead) for powering more than one highly rated appliance, such as an electric fire, is dangerous. (This is not the case for most fixed-wiring outlets to BS1363, which states that the standard rating of a double socket for use as part of the fixed wiring is 20 A.) Other "high-current" appliances such as washing machine and clothes dryer should ideally be fed from separate sockets for various reasons, but note that they do not use their full rated current at all times (in the cases of the Washing Machine and Dishwasher, for example, only when heating water which is a small percentage of the cycle).
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im talking about leads that are capable, of course. the power lead that came with my ps3 is thicker than the lead for my kettle (not just the outer)
 
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james.miller said:
im talking about leads that are capable, of course.
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Then using a lower rated fuse is just good practice as it would generate much quicker disconnection times which in turn reduce the chances of fire even further.

Devices have their own fuse's (clear glass quick blow ones normally) and the fuse's in plugs and extension leads are designed to protect the contacts and cables leading up too the device.


james.miller said:
im talking about leads that are capable, of course. the power lead that came with my ps3 is thicker than the lead for my kettle. the kettle is fitted with a 13a fuse, the ps3's came with a 3amp. why is that?
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The external thickness of the cable means nothing!! That could all be insulation for all you know, it's about the CSA of the copper cable inside the lead thats important.
 
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james.miller said:
im talking about leads that are capable, of course. the power lead that came with my ps3 is thicker than the lead for my kettle (not just the outer)
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Nice edit their ;)
I fail to see how you can determine the CSA of the copper unless you have cut off the moulded plug and stripped back cable or have x-ray vision like 'Superman' :p.
Either way the FACT of the matter is that the Fuse's in plugs and extensions are designed to protect the cable/contacts and NOT the devices connected too these cables.
Whether your man enough to admit you were wrong or not doesn't bother me so long as people are not mislead by your inaccurate information.
 
Now, now.
Can we perhaps agree that fuses are DESIGNED to protect the cable, but do very often offer some protection (against fire, if not fault damage) to the device hanging on the end of it?


BTW, not having opened a mains fuse....are they not TECHNICALLY fast-blows, rather than surge-proof (is that the right term?), in that, a 13A fuse WILL fail at 13A more or less instantly, rather than letting it go for a few secs like the surge-proof jobs you get in amplifiers/tvs/stuff with big capacitors to fill up when you switch on.
Maybe I'm oversimplifying and there's more than two types, or maybe the fast-blow/surge-proof distinction only exists for internal equipment fuses.

Funny, as long served audio engineer, I will take horrific liberties with signal cables, but never EVER do anything but by-the-book-with-belt-and-braces with mains. I'll happily dawdle about inside an instrument or computer that's powered up, but wont go within 6 feet of a lighting bar until I see the 3phase lead lying on the ground unplugged.

Oh, and I believe I menioned not running high loads though cables on drums or in coils because of the inductance, nasty RF hum, and eventually electric-fire-effect heating.

EDIT: asked a venue for an extension once, to solve some problem they'd created for me, and when I went to unroll it, after the first 10feet the cable was more or less a solid lump. Needless to say, I didn't use it.
 
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Super_Sonic said:
Nice edit their ;)
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i edited that post a 10 minutes before you replied, what's your point lol
I fail to see how you can determine the CSA of the copper unless you have cut off the moulded plug and stripped back cable or have x-ray vision like 'Superman' :p.
Either way the FACT of the matter is that the Fuse's in plugs and extensions are designed to protect the cable/contacts and NOT the devices connected too these cables.
Whether your man enough to admit you were wrong or not doesn't bother me so long as people are not mislead by your inaccurate information.
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and anyway what inaccurate information? how is saying 'its best to fuse for the appliance regardless of the ability of the cable' misleading anybody? it isnt, its just another level of safety. you can be anal about it you like:)
Super_Sonic said:
Then using a lower rated fuse is just good practice as it would generate much quicker disconnection times which in turn reduce the chances of fire even further.
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james.miller said:
an appliance could well destroy itself and combust pulling only 4 or 5 amps when the cable itself would have handled twice that. assume the worst case scenario, appliance combusts, fire spreads up the mains lead....the fuse isnt going to stop anything now, but had it been fused for the appliance in question, it might well have stopped the accident in the first place.
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exactly:) you can stick to your rulebook, that's fine. but fusing lower only aids in safety and when its mains voltage we're talking about, there's nothing wrong with that:)
 
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